by Srinivas Mahakud

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JPA
Java Persistence API

• by Srinivas Mahakud

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Review Topics

• Introduction
• what is the JPA?
• What is the JPA contains of?
• Why developers should Create the JPA?
• Is there Relationship between the EJB and JPA?
• What the JPA dose exactly?
• Sample process of java persistence API.
• Comparing between the EJB3 and the EJB2?
• What the advantages of using the JPA?
• what is my Tutorial ?
• Questions?

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Introduction

• One of the significant improvement in the java
  plate form is the JPA.
• This is because it offers developers much easier
  way to access and manipulate relational data in
  the java application.
• There is more than that .
• The reaction to the java persistence has been
  extremely positive from the java community
• JPA has had a good start with strong acceptance
  by the java developers.

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What is JPA?

• JPA stands for a java persistence API which is
  Javax. Persistence Package. Basically , it is a
  Java programming Language framework that helps
  developers to control relational data in java
  platform. The JPA exactly was described as part
  of the EJB3.0 , which is a replacement to the
  EJB2CMP Entity Beans specification, specification
  . As we know that a java persistence API is the
  newest of several Java persistence
  specifications.

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What is persistence consists of.. ?

• Any persistence consists of there Areas
• The API, defined in the Javax. Persistence
  package
• The java persistence Query Language
• Object / relational meta data.

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What JPA does exactly?

• JPA defined a runtime Entity Manger API
  processing queries and transaction on the objects
  against the database.
• It is defined a objects-level query language JPQL
  to allow querying of the objects from the
  database.

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What is java persistence query language is used
for?

• Basically, JPQL stands for Java Persistence Query
  Language. And it is used to make queries for
  against entities stored in a relational database.
  Queries resemble SQL queries in syntax, but
  operate against entity objects rather than
  directly with database tables.

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Is there relationship between the JPA and EJB?

• The answer is yes , there is a relationship
  between Java Persistence API(JPA) and Enterprise
  Java Beans (EJB).
• java persistence is a part of EJB which is it
  part of the Java EE5. Also, developers do not
  require EJB container in order to run
  applications, which use persistence. The API
  might be used outside the container within Java
  EE and can even stand alone in the Java Platform,
  Standard Edition (Java SE).

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Sample Process of Using Java Persistence API
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Why we should use the Java Persistence API?

• There is a great Motivation for creating JPA
• Many enterprise Java developers have been using
  lightweight persistent objects, which supported
  by open-source frameworks or data access objects
  as a substitute of entity beans. This is because
  entity beans and enterprise beans were too
  heavyweight and complicated. Furthermore, they
  could only be used in Java EE application servers.

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Comparing the EJB3 and the EJB2

• In fact, there are many differences, which are
  the advantages of EJB3.0, between the EJB 2.1
  version EJB 3.0 version

The EJB 3.0 EJB 2.1
Annotations and default replace a lot of cumbersome code. Persistence entities are simple concrete ,and plain old java object ( POJO)classes that developers can run as they would any other simple java technology classes The API provides capabilities , such as inheritance and polymorphism. Developers have to create lengthy, complicated ,and deployment descriptors in the application that use EJB technology. Developers have to implement the various abstract classes , interfaces, and interface methods whether they use them or not. Those capabilities are not available in the EJB2.0
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Example to illustrate more

• In the EJB 3.0 entity, java developers do not
  require to code interfaces such as
  LocalAddressHome and LocalAddress - or even a
  deployment descriptor. What they need to have
  just the entity class. This is because in the
  application's EJB 3.0 version, what's required
  for an entity has been reduced from three classes
  -- for local interfaces and a business class --
  to one entity class. In addition to that , they
  dont need to implement the EJBObject and
  EJBLocalObject interfaces. For instance, a
  session bean now need only a bean class and a
  business interface, which is a simple Java
  technology interface.

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Lets look to Another Example

• In this example, java developers can map a
  hierarchy of entities, where one entity
  subclasses another, to a relational database
  structure, and submit queries against the base
  class. The queries are treated polymorphically
  against the entire hierarchy.

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Summary of the Advantages of JPA

• JPA Requires Just smaller number of classes and
  interfaces
• It gets rid of lengthy deployment descriptors
  through annotations
• JPA Addresses most typical specifications through
  annotation defaults.
• JPA supports easier, cleaner, and standardized
  object-relational mapping.
• It add support for polymorphism, and inheritance.
• Also, dynamic queries and named queries is added
  to the JPA
• Supports a Java Persistence query language -- an
  improved EJB QL
• Makes it easier to test entities outside of the
  EJB container
• Can be used outside of the container